Founded in 1968 by Giuseppe Carnevale, Marmi Orobici Graniti S.p.A. of Bergamo, Italy, has maintained a pattern of growth over the years, and it is known worldwide as an international supplier of all stone varieties — producing and selling granite, marble and onyx slabs. Over the past decade, the demand for more exotic material has led Marmi Orobici to invest in technology to process these stones with optimal efficiency. The latest of these investments is an automated resin line using microwave technology.

In developing the technology, Pedrini worked on a machinery solution while Tenax worked on formulating the proper resin. It was implemented at Marmi Orobici in 2010. This investment has doubled the company’s capacity for producing resin-treated slabs, and it processes an average of 100 slabs per day or 10 to 15 slabs per hour.

The microwave process

The operating principle is based on the same concept as a microwave’s ability to heat food, water and other materials. It has already been utilized in production operations in other fields, and is now available to stoneworking plants.

At Marmi Orobici, slabs are treated with Tenax resin and fiberglass netting as needed, and then they enter the microwave unit, which works in conjunction with warm air ventilation. The slab automatically moves back and forth in the microwave unit for a few minutes (typically four minutes), and then it dries for one hour. With a traditional resin line, the resin-treated slabs are placed in a heated drier for two to three hours, and then cure for anywhere between 24 and 72 hours. During the process, while the resin and moisture in the stone is heated, the stone itself is actually not heated.

In addition to speed, the use of microwave technology adds to the effectiveness of the resin application. When placed in the microwave unit, the resin becomes hot and flowing, as opposed to a typical vacuum resin-application system. Because the resin reaches a lower viscosity, it penetrates deeper into the slab.

The resin line was custom built for Orobici, and it features PLC control with software that allows quick adjustment of all processing parameters. Each slab is positioned on a closed-structure tray, where it lays during all the different operations — pre-heating, resining and resin curing. To ensure operator safety, detectors are in place to sound an alarm if any microwaves escape from the unit.

The Tenax resin product used at Marmi Orobici has a completely different formulation than its traditional epoxy resin, as it needs to work with the unique technical parameters of a microwave oven.

In addition to increased speed and efficiency, there is less handling of the slabs required between treatment and polishing, resulting in lower manpower and less breakage. At Marmi Orobici, only three workers are required to work on the microwave resin line — two to apply the resin and one working the machine.

Prior to being processed on the resin line, raw slabs are produced using two Pedrini multi-wire saws — one with 24 wires and another with 40 wires — as well as multiple gangsaws. Meanwhile, automatic slab polishing and calibrating is done on units from Pedrini and Breton, which are equipped with Tenax abrasives.

With a global presence in the stone market, Marmi Orobici ships its finished products to destinations around the world, and it lists the U.S. among its major export targets.